The big twist of Return of the Jedi was Luke and Leia were actually siblings, and the Princess had her own sensitivity to The Force.
James Earl Jones’ comments to THR indicate that the actor knew another shoe was going to drop in the Star Wars franchise.
Instead of Darth Vader proving not to be Luke’s father, he actually became the parent to another one of the franchise’s heroes: Leia.
The galaxy far, far away usually contains at least one big WTF moment per episode, making the plot as important as the epic lightsaber duels and space battles.